1. Field of the Invention
The present invention relates to a backlight unit and a liquid crystal display (LCD) device module and more particularly to a backlight unit including a light emitting diode (LED) assembly having a reduced width, and a liquid crystal display device module including the backlight unit.
2. Discussion of the Related Art
The LCD device, which uses an optical anisotropy and a polarization property to display an image, is widely used for notebook computers, monitors, TV, and so on, because of their high contrast ratio and characteristics adequate to display moving images.
The LCD device includes a liquid crystal panel having a first substrate, a second substrate and a liquid crystal layer. The first and second substrates face each other, and the liquid crystal layer is interposed therebetween. An arrangement of the liquid crystal molecules in the liquid crystal layer is changed by an electric field induced in the liquid crystal panel to control light transmissivity.
Generally, an additional light source is required because the LCD panel is a non-emissive-type display device. Accordingly, a backlight unit is disposed under the LCD panel. The LCD device displays images using light produced by the backlight unit and supplied to the LCD panel.
FIG. 1 is a cross-sectional view of the related art LCD device module. In FIG. 1, the LCD device module includes a liquid crystal panel 10, a backlight unit 20, a main frame 30, a top frame 40 and a bottom frame 50.
The liquid crystal panel 10 includes a first substrate 112, a second substrate 14 and a liquid crystal layer (not shown). The first and second substrates 12 and 14 face each other, and the liquid crystal layer is interposed therebetween. First and second polarization plates 19a and 19b is disposed on opposite sides of the liquid crystal panel 10.
The backlight unit 20 is disposed under the liquid crystal panel 10. The backlight unit 20 includes a light source 29, a reflective sheet 25, a light guide plate 23 and an optical sheet 21. The light source 29 is arranged along at least one side of the main frame 30. The reflective sheet 25 is disposed on the bottom frame 50 and has a color of white or silver. The light guide plate 25 is disposed on the reflective sheet 25, and the optical sheet 21 is disposed on or over the light guide plate 23.
The liquid crystal display panel 10 and the backlight unit 20 are combined using the main frame 30 that can prevent movement of the liquid crystal panel 10 and the backlight unit 20. The top frame 40 cover edges of the liquid crystal panel 10 and sides of the main frame 30, so the top frame 40 can support and protect of the edges of the liquid crystal panel 10 and sides of the main frame 30. The bottom frame 50 covers back edges of the main frame 30, so the bottom frame 50 is combined with the main frame 30 and the top frame 40 for modulation.
One of a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp and an LED is used as a light source 29 of the backlight unit 20. Among these light source, the LED is widely used because of their characteristics, for example, small size, low power consumption, and so on.
As shown in FIG. 1, the LED 29a is arranged on a printed circuit board (PCB) 29b to form the light source 29. The light source 29 including the LED 29a may be referred to as an LED assembly. The light emitted from at least one LED assembly 29 is provided into the light guide plate 23. The light is processed into a plane light source having an uniform brightness through the light guide plate 23, the reflective sheet 25 and the optical sheet 21, and provided into the liquid crystal panel 10. Power is provided into each LED 29a through a power line (not shown) on the PCB 29b. All LEDs 29a are turned on and off such that white light is obtain by mixing red, green and blue light.
Although not shown, a backlight driving circuit for controlling the LED assembly 29 is disposed on the LCD device module. The backlight driving circuit is bent into a rear surface of the bottom frame 50 to minimize a size of the LCD device module. A pad unit, which is connected to the backlight driving circuit through a cable, may be formed on the PCB 29b such that the LED assemblies 29, which are linked to each other, may be connected to the backlight driving circuit. Since the LEDs 29a in parallel receives power, the number of the pad units on the PCB 29b may be same as the number of the LEDs 29a. As there are more pad units, a width (a vertical thickness in FIG. 1) is increased.
On the other hand, since the LED assembly 29 is vertically positioned at a side of the bottom frame 50, a thickness of the backlight unit 20 is determined by a thickness “d1” of the PCB 29b of the LED assembly 29. Accordingly, as there are more pad units, the LCD device module has an increase thickness.